This invention relates to the drainage of aqueous humor from eyes in the course of relieving eye disorders. Specifically, the invention relates to an implant which, when permanently affixed to or implanted in a specific area of the eye, will provide such drainage efficiently, for longer periods than heretofore accomplished, and, in short, will provide relief and prevent, or at least postpone, the adverse ultimate effects of glaucoma. The present invention also relates to a method for inserting the implant, and a surgical device for inserting the implant.
The eyeball is composed of three basic layers: (1) the sclera; (2) the middle layer or choroid; and (3) the retina. The sclera 10 is the outer layer of the eyeball. It consists of tough, white tissue that serves as the supporting framework of the eye. At the front of the eye, the sclera is continuous with the clear, transparent cornea 20 through which light enters the eye. The clarity of the cornea is maintained by the delicate layer of cells on the posterior side thereof, called the endothelium 30. If a foreign material, such as plastic, metal, hydrogen, silicon, etc., touches the endothelium, these cells will die. However, because of the nature of the endothelium cells, which are designed to pump fluid out of the cornea, the death of these cells can impair the vision of the eye. The corneal endothelial cells have tight junctions between them so that fluid will not leak into the cornea and thus need to be pumped out. Should an endothelial cell die, the adjacent cells will expand their size and grow together to reform the tight junction to effect a seal. When such a cell dies, other endothelial cells will migrate and expand into the area previously occupied by the dead cell. A device or other foreign object placed into the trabecular meshwork area of the anterior chamber of the eye should be less than 20 microns in external diameter to avoid touching the corneal endothelium. If the device touches the endothelium, progressive endothelial cell loss will occur, causing the cornea to cloud, causing loss of vision and ultimately for the need for a corneal transplantation. Behind the cornea is a small space, the anterior chamber, which contains a clear watery fluid called the aqueous humor.
The middle layer is composed of three parts: (1) the choroids; (2) the ciliary muscle 310; and (3) the iris 40. The choroid lies behind and to the sides of the eyeball making up about 80% of the middle layer. It contains most of the blood vessels that nourish the eye.
Toward the front of the eyeball, the choroid becomes the ciliary muscle 310. This muscle is connected by fibers to the lens 50, keeping the lens in place and controlling its shape. At the very front, the middle layer becomes the iris, a thin curtain of tissue in front of the lens. A round opening in the iris, whose size is controlled by muscles in the iris, is called the pupil 60.
In simple terms, the cornea refracts light through the anterior chamber 70 and then through the pupil, the entrance aperture of the eye to the lens. The lens serves to focus the refracted light through the vitreous chamber 80 containing the vitreous humor onto the retina, the rear surface of the eye.
As shown in FIGS. 1-3, normally the fluid within the eye, the aqueous humor, is produced by the ciliary body 90 and migrates through the pupil into the anterior chamber, the small space behind the cornea. From this chamber, the liquid migrates through the trabecular meshwork 100 through Schlemm's canal 115 and into the aqueous veins which form fluid collection channels beneath the conjunctiva 150, the latter covering the front of the eyeball except for the cornea.
When the aqueous, migration, described above, is insufficient to relieve the build-up of intra-ocular pressure, glaucoma results. This pressure build-up is usually thought to be due to one or more obstructions in the trabecular meshwork through drainage areas behind the trabecular meshwork which can also impede flow of fluid out of the eye. Unless controlled, the high pressures associated with glaucoma ultimately leads to permanent damage of the optic nerve, the nerve formed from the sensitive fibers of the retina.
The prior art shows many implantable devices and methods of implanting them, but the majority violate the wall of the sclera adjacent to the vascular tissue of the conjunctiva. Such violation causes stimulation of vascular tissue. The majority of the prior art also discloses methods and devices that violate the corneal endothelium.
The prior art disclosed an approach to avoid the problem of fluid pressure buildup that involved implanting a device in the sclera. It was noted in surgical studies that the intraocular pressure would drop significantly with the use of this type of device but that over time some eyes would have a rise in intraocular pressure corresponding to a clinical trapping of the aqueous fluid around the implant in the sclera. The sclera is a non-reactive tissue; it only heals when vascular tissue from above or below grows into it. The sclera is also composed of a meshwork of fibrous tissue with passageways or spaces as large as 150 microns. The present invention provides an improved insertable device and a method of inserting such a device into the sclera without causing the conjunctiva to heal and thus block the fluid egress created by the device.
The object of the present invention is to provide a device that can be implanted permanently, simply and effectively to permit substantially normal migration of fluid out of the anterior chamber of the eye and, thus, avoid the abnormal build-up of intra-ocular pressure. Another object is to provide the implant in a manner that will also avoid excessive migration of fluid that would lead to collapse of the anterior chamber with its accompanying complications.
Another object of the present invention is to provide a device and method of implanting the device that eliminates the problem of healing of the conjunctiva and tenon's tissue. Another object of the invention is to provide an implant or insertable device and a method of inserting the implant or device that prevents it from contacting the corneal endothelium. Finally, another object of the invention is to provide a device that is deformable and recoverable to allow it to pass through multiple incisions.